Die Rolle des DDR1 beim Glioblastoma multiforme

Glioblastoma multiforme (GBM) is not only the most aggressive (WHO Grade IV) but also the most common type of malignant brain tumors. The current standard GBM therapy consists of a maximal and safe resection of the tumor, followed by combined adjuvant therapy with radiation and chemotherapy using temozolomide (TMZ). Despite this intense therapy regimen, GBM still has a bad prognosis with a median survival rate of only 14-15 months. It is an accepted concept that in GBM tumor cells can interact with collagen, a component of the extracellular matrix. In particular, tumor stem cells in GBM (GBM SCs) can anchor to collagen-rich niches in order to protect themselves against treatment-induced cell death. This thesis examines the role of the collagen receptor Discoidin-Domain-Receptor 1 (DDR1), for the interaction between GBM SCs and collagen. The localization of GBM SCs in a collagenous environment and their abundant DDR1 expression was confirmed with immunohistochemistry. Moreover, the aberrance of GBM SC and DDR1 expression status in patient-matched samples, which consist of tissue of primary and recurrent tumor, was analyzed. No significant difference, however, of DDR1 expression and accumulation of GBM SCs between both tumor tissues was found. In order to prove DDR1 expression as a distinctive feature of the stem cell phenotype, DDR1 expression levels on protein and messenger RNA (mRNA) were analyzed by immunofluorescence and quantitative real-time polymerase chain reaction (qPCR), respectively. For this analysis, primary human GBM SCs, cultivated both under stem cell conditions and differentiation conditions, were used. The difference in DDR1 expression between both types of cells was minor and most prominent at the DDR1 localization at the cell membrane. However, there was no quantitative difference in DDR1 gene expression as determined by qPCR. In addition, the inhibitory effect of a DDR1 inhibitor on primary human GBM SCs was evaluated by western blot using an antibody against phosphorylated DDR1. This analysis however yielded no useful results as a consequence of problems establishing this method. Taken together, the results of this work give rise to further examinations, especially for functional studies with dose-response curves to compare a combined therapy including DDR1 inhibitor and TMZ with a monotherapy consisting of TMZ only to investigate an eventual advantage of combined treatment. This might provide the scientific base to enhance the efficacy of antineoplastic chemotherapy.